Avoid destroying surface before the parent surface stops referencing it.

cc/surfaces/surface_sequence.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_SURFACES_SURFACE_SEQUENCE_H_
+#define CC_SURFACES_SURFACE_SEQUENCE_H_
+
+namespace cc {
+
+// A per-surface-namespace sequence number that's used to coordinate
+// dependencies between frames. A sequence number may be satisfied once, and
+// may be depended on once.
+struct SurfaceSequence {
+  SurfaceSequence() : id_namespace(0u), sequence(0u) {}
+  SurfaceSequence(uint32_t id_namespace, uint32_t sequence)
+      : id_namespace(id_namespace), sequence(sequence) {}
+
+  uint32_t id_namespace;
+  uint32_t sequence;
+};
+
+inline bool operator==(const SurfaceSequence& a, const SurfaceSequence& b) {
+  return a.id_namespace == b.id_namespace && a.sequence == b.sequence;
+}
+
+inline bool operator!=(const SurfaceSequence& a, const SurfaceSequence& b) {
+  return !(a == b);
+}
+
+inline bool operator<(const SurfaceSequence& a, const SurfaceSequence& b) {
+  if (a.id_namespace != b.id_namespace)
+    return a.id_namespace < b.id_namespace;
+  return a.sequence < b.sequence;
+}
+
+}  // namespace cc
+
+#endif  // CC_SURFACES_SURFACE_SEQUENCE_H_